At present, in order to treat spinal diseases such as degenerative disorders, spinal trauma, spinal tumor, spinal deformity and the like, a method of transpediclular internal fixation is widely used all over the world, with satisfactory results. The multi-axial pedicle screw traditionally used, in common international circumstances, has a structure wherein the entire screw-thread is a solid structure. The fixation strength of such a screw depends on the contact area of the screw-thread and the bone, as well as the strength of the vertebrae per se. However, it is usually not possible to maintain a strong fixation strength in a slipped vertebrae reduction during fixation and to sustain such a holding force after fixation. As a result, a failure of vertebrae reduction and fixation, or unsatisfied anatomical reduction, may occur, thus, missing the goal of the surgery. Especially, a failure due to an operated screw loosening, or even pulling out, often occurs when patients suffer osteoporosis or perform improper activities after surgery.
Previously, the Chinese utility model patent number 03262479.4 disclosed an expansion method by using an expandable screw, comprising a barrel-shaped outer cannular screw, and a gauge screw. A screw thread and square, for holding, are set at the end. Four uniformity expansion parts are cut on the tip of the outer cannular screw along its axis. The contact mechanics of the pedicle screw and the vertebrae is changed by means of a mechanical expansion provided by the utility model patent. Thus, the contact mechanics of the screw and screw path is changed when adjustments are made to the gauge screw for effectively improving fixation strength. Moreover, Chinese utility model patent number 03235808.3 disclosed another kind of hollow pedicle screw having a connecting screw thread on both its inner and outer walls, and an expansion screw rotationally installed in a cavity of the vertebral arch pedicle screw. The lower part of the cavity of the vertebral arch pedicle screw is an inner cavity structure having at least three expanding gaps extending vertically downwards along its wall and having an end for holding. The purpose of the utility model patent is to increase fixation strength (anti-pulling out) of the pedicle screw. Disadvantages of both patents are that the gauge screw (expansion screw) is uneasy to insert in a manner that allows for adjustments during an operation. Also, operating steps for a surgeon to insert and fix the end part of a pedicle screw with other components is mono-directional, which contradicts the multi-directional and multi-angular demands of an inner spinal fixing operation. Furthermore, a degree of adjustment needed in a gauge screw operated by surgeons differs in fulfilling different expandable methods, and differences of expandable degree also occur between screws, which influences the treatment effectiveness and uniformity of a pedicle screw product.